1. Field of the Invention
The foam cleaning system of this invention has particular application to the cleaning of two-stage electrostatic precipitators. A typical precipitator will include an ionizer unit having a plurality of ground plates between which are located ionizing wires. It will also include a collecting cell having support members for a plurality of grounded collecting plates and a plurality of charge collecting plates interleaved among the grounded collecting plates. The ionizer and collecting cell may be combined. In any event the stream of air passing through the precipitator first encounters the ionizer and then the collecting cell. In the practice of the instant invention a filter is provider at the inlet side of the precipitator, i.e., adjacent the exterior side of the ionizer, and another filter is provided at the outlet side of the precipitator, i.e., adjacent the exterior side of the collecting cell. 2. Description of the Prior Art
In the past, in some instances, in cleaning electrostatic precipitators, it has been necessary to dismantle the precipitator and to take out the various filters, plates and the like and soak them for an extended period of time or subject them to steam cleaning and the like. In practice the prior art has also cleaned the precipitator in place by using vast quantities of hot water and detergent spray introduced into the precipitator with no penetration time period being provided. The prior art spray, as distinguished from foam, had difficulity in reaching all of the plates and insulator surfaces. This was a serious defect because if contaminants were permitted to form a conductive bridge across any two of the adjoining cell plates within a precipitator module, that module would be rendered inoperative.
Foam generating units of the type employed in the practice of this invention were also known to the prior art; the prior art workers, however, did not know how to incorporate such foam generating units for the cleaning of two-stage electrostatic precipitators, all as will be developed further herein.
Although no search for the prior art has been made, in addition to the systems just mentioned, which are generally used for cleaning precipitators which have relieved air of hydrocarbons, or "wet" contaminants, it is known that some cleaning of electrostatic precipitators can be accomplished by the application of vibrations to the various plates to rid them of "dry" contaminants. With respect to that type of cleaning the following United States Patents are pertinent to some extent: Palmer U.S. Pat. No. 2,490,979; Burton U.S. Pat. No. 2,842,938; Forbes U.S. Pat. No. 1,630,482; and Steuernagel U.S. Pat. No. 3,113,852. Cheney et al. U.S. Pat. No. 4,057,405 entitled "MEANS FOR THE CLEANING AND SELF-CLEANING OF AN ELECTROSTATIC PRECIPITATOR" is also directed to a two-stage electrostatic precipitator in which the plates are rid of a certain amount of dry contaminants by the application of variable frequency vibrations thereto.
In all of the known prior art electrostatic precipitators it has eventually become necessary to subject the unit to a thorough cleaning which goes beyond that accomplished by the various sprays (non-foaming) and vibrating means aforementioned. The instant invention permits such thorough cleaning to take place in situ. It is not necessary to dismantle the precipitators.